1. Field of the Invention
A anti-virus  A protection system for use within a data transmission network to protect against the transfer of viruses from a source(s) or originator(s) to a recipient(s) or subscriber(s) over the data transmission network.
2. Description of the Prior Art
With the advent of data transfer over communication networks, computer viruses, worms and Trojan horses have plagued and compromised the operation of the various computers or nodes. A computer virus is a section of code that is buried or hidden in another program attaching itself to other programs in the system that, in turn, can be copied over to other programs. Such viruses can cause a message to be displayed on the screen or actually destroy programs and data. Worms, on the other hand, are destructive programs that replicate themselves using up computer resources  resources, eventually causing the computer system to crash.
The prior art has attempted to reduce the effects of viruses and eliminate the proliferation through virus detection programs. For example, an operator can monitor a computer or system for such basis  basic operating functions such as write, erase or format disk. When such operations occur, the user is prompted to confirm whether the operation is expected. If the particular operation or function is not expected, the user aborts the operation as having been prompted by a virus program. Another virus detection method,  method scans program code being copied onto the system searching for recognizable patterns of program code used for viruses. Another method employs check summary on host programs known to be free from viruses. If a virus later attaches itself to a host program, the value will be different and the presence of a virus detected.
Unfortunately, despite these efforts of  efforts, the prior art suffer  suffers from various deficiencies. Therefore, there is a need for a system and method for effectively detecting and eliminating viruses without significantly affecting the performance of the computer. Behavior interception is not successful at detecting all viruses since a virus can be placed at locations where such  critical operations are likely to occur for the normal operation of programs. Second, most signature scanning is only performed on new inputs from disk drives. With the advent of the Internet and its increased popularity, there are no prior art methods that have been able to successfully scan connections such as those utilized by a gateway node in communicating with other networks. Third, many of the above methods require a significant amount of computing resources, which in turn degrades the overall performance of the system. Thus, operating the  virus detection programs on every computer becomes impractical. Therefore, the operation of many such virus detection programs is disabled for improved performance of individual machines.
U.S. Pat. No. 5,623,600 discloses a system for detecting and eliminating viruses on a computer network that includes a File Transfer Protocol (FTP) proxy server, for controlling the transfer of files  files, and a Simple Mail Transfer Protocol (SMTP) proxy server  server, for controlling the transfer of mail messages through the system. The FTP proxy server and SMTP proxy server run concurrently with the normal operation of the system and operate in a manner such that viruses transmitted to or from the network in files and messages are detected before transfer into or from the system. The FTP proxy server and SMTP proxy server scan all incoming and outgoing files and messages respectively before transfer  messages, respectively, for viruses before transfer, and then transfer the files and messages, only if they do not contain any viruses. The method for processing a file before transmission into or from the network includes the steps of receiving the data transfer command and file name; transferring the file to a system node; performing virus detection on the file; determining whether the file contains any viruses; transferring the file from the system to a recipient node if the file does not contain a virus; and deleting the file if the file contains a virus.
U.S. Pat. No. 6,157,721 and U.S. Pat. No. 6,292,569 describes a system and method  describe systems and methods using cryptography to protect Secure  secure computation environments from bogus or rogue load modules, executables  executables, and other data elements through use of digital signatures, seals  seals, and certificates issued by a verifying authority. The verifying authority tests the load modules or other executables to verify that the corresponding specifications are accurate and complete, and then digitally signs the load module or other executable based on tamper resistance work factor classification. Secure computation environments with different tamper resistance work factors use different verification digital signature authentication techniques allowing one tamper resistance work factor environment to protect against load modules from another, different tamper resistance work factor environment. Several dissimilar digital signature algorithms may be used to reduce vulnerability from algorithm compromise, and subsets of multiple digital signatures may be used to reduce the scope of any specific compromise.
U.S. Pat. No. 5,416,842 teaches a first data processing device (node I) coupled to a first private network and to a firewall server (FWA). Firewall server FWA is in turn coupled to a public network such as the Internet. A second data processing device (node J) is coupled to a second private network that is coupled to the Internet through a firewall server (FWB). Node I provides a data packet  packet, including IP data and a destination address for the intended receiving node J  J, to the firewall FWA. The firewall FWA is provided with a secret value a,  “a,” and a public value. The firewall FWB is provided with a secret value “b,” and a public value. The firewall FWA obtains a Diffie-Hellman (DH) certificate for the firewall FWB and determines the public value from the DH certificate. Firewall FWA then computes the value and derives a key K. ( Kab) from the value .varies.sup.ab mod p.  p (∝ab mod p). A transient key K. (Kp) is randomly generated and is used to encrypt the data packet to be transmitted by firewall FWA to firewall FWB. The encrypted data packet is then encapsulated in a transmission packet by the firewall FWA. The transmission packet includes an unencrypted destination address for the firewall FWB. Firewall FWA then sends the transmission packet to firewall FWB over the Internet. Upon receipt of the transmission packet from firewall FWA, firewall FWB obtains a DH certificate for firewall FWA, and determines the public value of from the DH certificate. Firewall FWB computes the value of .varies.sup.ab mod p,  (∝ab mod p), and derives the key K.sub.ab. (Kab). Firewall B utilizes the key K.sub.ab (Kab) to decrypt the transient key K. and  (Kp), using the decrypted transient key K. (Kp), firewall FWB decrypts the encrypted data packet received from FWA, thereby resulting in the recovery of the original data sent by node I in unencrypted form to the firewall FWA. The firewall FWB then transmits the decrypted data packet to the receiving node J over the second private network.
U.S. Pat. No. 5,432,850 shows a method for secure transmission of data having a destination address and a source address on a shared communication network. The method comprise the steps of  of: transmitting a multiplicity of data frames, each containing at least an encrypted data sequence employing the destination address as at least part of a decryption key therefor,  therefor; receiving the multiplicity of data frames at a receiver on the shared communication network  network; and attempting to decrypt the encrypted data sequence by employing the local address of the receiver as at least part of a decryption key.
U.S. Pat. No. 5,511,122 relates to an internet authentication method to verify a sending host by a receiving host or an intermediate router or gateway. The method comprises the steps of: obtaining a network address and a public key of a receiving host; utilizing the public key from the receiving host in combination with a private key of the originating host to generate a cryptographic signature; transmitting the signature along with data through a first subnetwork in at least one packet; receiving at least one packet at the receiving host; and the receiving host utilizing a private key of said receiving host site and a public key of said originating host to verify said cryptographic signature.
U.S. Pat. No. 6,065,118 shows a system to reduce the risk of damage to data or programs in an end user computer system programmed to operate in response to an imported data stream containing one or more mobile program components from an external source. The incoming data stream is screened to identify mobile program components of that data stream. Some  Prior to being executed, some of the mobile program components are passed to a program execution location isolated from the end user system prior to being executed  to operate in a desired manner. The execution location has an interface with the external source of the data stream and an interface with the end user system. The operation of the interface between the execution location and the end user system is programmed so that only data that has been interacted on by the program component within the execution location in a specified and controlled manner can be passed to and from the end user system.
U.S. Pat. No. 6,067,620 describes a secure network interface unit (SNIU) to provide multi-level security on a network having a plurality of secured and unsecured users including  including: network interface means for communicating on the network,  network; identifying the source and destination of a message intercepted on the network; determining the security levels of each of the plurality of users; a trusted computing base for determining whether the message, if transmitted to the destination user, will violate security parameters; and,  cryptographically encrypting messages sent to, and decrypting messages received from  from, another SNIU affiliated with the destination user.
U.S. Pat. No. 6,108,583 shows a system and method for data communication with adaptive security in which a send host transmits a data stream to a receive host in packets which contain an authentication data block with an authentication header and a signature block. The authentication header advantageously contains various fields including a verification type, a security algorithm, a minimum security level, a target security level, and an actual security level. The receive host adaptively performs verification of the data packets using varying security levels based in part on the availability of security operations per second (SOPS) in the receive host. Where a data stream in the receive host is delayed by a security processing bottleneck, the receive host may alter the verification type, security algorithm, or the actual security level to speed up the processing of the data stream by reducing the amount of security processing performed. The receive host further allocates the SOPS among the data streams received.
U.S. Pat. No. 6,229,806 describes a communication system in which a user device generates authentication information unique to the user device and provides a data packet including this authentication information to an infrastructure part which is a gateway or a host. The packet also contains a host identifier or time dependent information. This is used at the gateway or the host to authenticate the packet.
U.S. Patent Application Publication No. 2002/0023214 shows how secure computation environments are protected from bogus or rogue load modules, executables  executables, and other data elements through use of digital signatures, seals  seals, and certificates issued by a verifying authority. A verifying authority tests the load modules or other executables to verify that their corresponding specifications are accurate and complete, and then digitally signs the load module or other executable based on a tamper resistance work factor classification. Secure computation environments with different tamper resistance work factors use different verification digital signature authentication techniques, e.g. different signature algorithms and/or signature verification keys, allowing one tamper resistance work factor environment to protect itself against load modules from another, different tamper resistance work factor environment. Several dissimilar digital signature algorithms may be used to reduce vulnerability from algorithm compromise, and subsets of multiple digital signatures may be used to reduce the scope of any specific compromise.
U.S. Patent Application Publication No. 2002/0040439 teaches a system and method for providing external data signal isolation, and signal-level information-preserving-data-transformations, to enable safe, operationally efficient, information sharing between protected information systems and networks and external, potentially hostile, information systems and networks  networks, which neutralizes  neutralize any imbedded hostile executable codes such as viruses that may be in data-signals incoming from the external systems and networks. The system and method prevent untransformed external data-signals from entering protected systems and/or networks using an intermediate screen that is a computer hardware device. The intermediate screen, which may be implemented as a network of systems, is deployed between the protected systems and external systems and is used to process all incoming signals from the external system  systems to obtain transformed data sets from which information is extracted before it is passed to the protected system  systems. The incoming signals all remain confined in the intermediate screen.